That is probably the "tear-off tabs" feature. A slight movement (usually downward) when clicking on an existing tab will cause that tab to "tear-off" and open in a new window. You can drag the tab back to the previous window. You can also install this add-on to stop the behavior: https://addons.mozilla.org/en-US/firefox/addon/bug489729-disable-detach-and-t/ <br /> -------------------------- <br /> '''You need to update the following.''' The Plugin version(s) shown below was/were submitted with your question and is/are out of date. You should update to avoid known security issues with the version(s) you have installed. Click on "More system info..." to the right of your question to see what was included with your question. *Adobe Shockwave for Director Netscape plug-in, version 11.5.9.615 *Next Generation Java Plug-in 1.6.0_20 for Mozilla browsers #'''''Check your plugin versions''''' on either of the following links': #*http://www.mozilla.com/en-US/plugincheck/ #*https://www-trunk.stage.mozilla.com/en-US/plugincheck/ #*'''Note: plugin check page does not have information on all plugin versions''' #*There are plugin specific testing links available from this page: #**http://kb.mozillazine.org/Testing_plugins #'''Update Shockwave for Director''' #*NOTE: this is not the same as Shockwave Flash; this installs the Shockwave Player. #*Use Firefox to download and SAVE the installer to your hard drive from the link in the article below (Desktop is a good place so you can find it). #*When the download is complete, exit Firefox (File > Exit) #*locate and double-click in the installer you just downloaded, let the install complete. #*Restart Firefox and check your plugins again. #*'''<u>Download link and more information</u>''': http://support.mozilla.com/en-US/kb/Using+the+Shockwave+plugin+with+Firefox #'''Update the [[Java]] plugin''' to the latest version. #*Download site: http://www.oracle.com/technetwork/java/javase/downloads/index.html (Java Platform: Download JRE) #**'''''Be sure to <u>un-check the Yahoo Toolbar</u> option during the install if you do not want it installed. #*Also see "Manual Update" in this article to update from the Java Control Panel in Windows Control Panel: http://support.mozilla.com/en-US/kb/Using+the+Java+plugin+with+Firefox#Updates #* Removing old versions (if needed): http://www.java.com/en/download/faq/remove_olderversions.xml #* Remove multiple Java Console extensions (if needed): http://kb.mozillazine.org/Firefox_:_FAQs_:_Install_Java#Multiple_Java_Console_extensions #*Java Test: http://www.java.com/en/download/help/testvm.xml